1. Field of the Invention
The present invention relates to an infrared detector and, in particular, relates to a thermal infrared detector having a heat insulation structure section.
2. Background Art
FIG. 10 is a sectional view of an infrared detector disclosed in Japanese Patent Laid-Open No. 10-209418. In the infrared detector of FIG. 10, an insulating film 2, such as SiO2 is formed on a silicon substrate 1. In the insulating film 2, there are a heat detection section 3, such as bolometer; and a metal wiring 4 connected to the heat detection section 3.
Further, the silicon substrate 1 below the heat detection section 3 is provided with a hollow section 6, thereby making a vicinity of the heat detection section 3 into a heat insulating structure section 7.
Above the heat detection section 3, there is provided a plate-like infrared absorption section 9 supported by a support section 5 such as SiO2. The infrared absorption section 9 comprises an insulating layer 10, an infrared absorption film 11 on a surface of the insulating layer 10, and an infrared reflection film 12 on a rear surface of the insulation layer 10. Infrared light incident on the infrared detector is absorbed by the infrared absorption section 9 and thereby converted into heat, and is transmitted to the heat detection section 3 through the support section 5. In the heat detection section 3, a thermal change due to such a heat is detected. Thus, the incident of infrared light on the infrared absorption section 9 is detected. In the structure shown in FIG. 10, infrared absorption efficiency is increased by providing the infrared reflection film 12 on the rear surface of the insulation layer 10 to thereby reflect the infrared ray transmitted through the infrared absorption film 11 and causing it to come into the infrared absorption film 11 again.
However, in order to manufacture the infrared detector with high sensitivity, it is further necessary to increase the infrared absorption efficiency in the infrared absorption section 9. Contrary to this, it is known that the infrared absorption efficiency is increased by adopting an optical cavity structure in which an optical distance between the infrared absorption film 11 and the infrared reflection film 12 is set to one quarter of the center wavelength of the infrared light absorbed.
However, in order to make the infrared detector of FIG. 10 into an optical cavity structure, the thickness of the insulating layer 10 sandwiched between the infrared absorption film 11 and the infrared reflection film 12 must be on the order of 1 xcexcm, so that the heat capacity of the infrared absorption section 9 becomes large. Therefore, the thermal time constant in heat detection section becomes large, so that there has been a problem that infrared detection following a rapid temperature change becomes impossible.
Accordingly, an object of the invention is to provide a high sensitivity infrared detector with no increase in heat capacity of the infrared absorption section, and to provide, in particular, a detector having an optical cavity structure.
This object and advantages of the invention are achieved by providing a novel and improved infrared detector, and the infrared detector is an infrared detector for detecting an absorbed infrared ray by converting it into heat, comprising: a semiconductor substrate having a heat insulation section; a heat detection section provided in the heat insulation section; an infrared absorption film disposed substantially parallel to a surface of the semiconductor substrate with a predetermined spacing being kept from the surface; and an infrared reflection film provided on the semiconductor substrate; wherein an infrared ray having transmitted through the infrared absorption film is reflected by the infrared reflection film and comes into the infrared absorption film again.
Further, according to one aspect of the invention, there is provided a method of producing an infrared detector for detecting an absorbed infrared ray by converting it into a heat, comprising the steps of forming, on a semiconductor substrate, a wiring layer and a heat detection section connected to the wiring layer, and covering them with an insulation film; forming an infrared reflection film on the insulation film; forming a sacrifice film on the infrared reflection film, and forming an opening portion in the sacrifice film above the heat detection section, thereby exposing the infrared reflection film; forming, on the sacrifice film, an infrared absorption section including an infrared absorption film; removing the sacrifice film; and forming, below the heat detection section, a hollow section by etching the semiconductor substrate.
Furthermore, according to another aspect of the invention, there is provided a method of producing an infrared detector for detecting an absorbed infrared ray by converting it into a heat, comprising the steps of forming a metal layer on a semiconductor substrate, and forming a wiring layer and an infrared reflection film separated from the wiring layer by patterning the metal layer; forming a heat detection section connected to the wiring layer, and covering it with an insulation film; forming a sacrifice film on the insulation film, and forming an opening portion in the sacrifice film above the insulation film, thereby exposing the insulation film; forming, on the sacrifice film, an infrared absorption section including an infrared absorption film; removing the sacrifice film; and forming, below the heat detection section, a hollow section by etching the semiconductor substrate.
The above object and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly appear, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits of the invention.
Thus, as a result of intensive study, the inventors has found the fact that the infrared absorption efficiency can be increased without increasing the thermal time constant by means of forming an optical cavity structure by providing an infrared reflection film on a semiconductor substrate and using such an infrared reflection film and an infrared absorption film provided in an infrared detection section, and thereby the invention has been completed.